This invention relates to processes for making bis(3-hydroxypropyl) dicarboxylate monomer such as bis(3-hydroxypropyl) terephthalate and bis(3-hydroxypropyl) naphthalenedicarboxylate monomers from C1-C4 dialkyl esters of terephthalic acid or naphthalene dicarboxylic acid and 1,3-propanediol in the presence of a yttrium or samarium compound transesterification catalyst.
Preparation of polyester resins by transesterification of a C1-C4 dialkyl ester of terephthalic acid and a diol or of a C1-C4 dialkyl ester of naphthalene dicarboxylic acid acid and a diol, followed by polycondensation is well known in the art.
Generally, the C1-C4 dialkyl ester of terephthalic acid or naphthalene dicarboxylic acid and the diol are reacted in the presence of a transesterification catalyst at elevated temperature and atmospheric pressure to form a monomer and a C1-C4 alkanol corresponding to the C1-C4 alkanol components of the dialkyl ester. The C1-C4 alkanol is removed as it is formed during the reaction. Oligomers having a degree of polymerization of about 4 or less can also be formed. The monomer and any oligomer can then be polymerized at higher temperatures under reduced pressure in the presence of a polycondensation catalyst to form the desired polyester resin. These reactions can be carried out in batch or continuous processes.
Transesterification catalysts known in the art include titanium, manganese, lanthanum and zinc compounds. For example, U.S. Pat. No. 3,671,379 to Evans et al., discloses a process for producing poly(trimethylene terephthalate) using a titanium catalyst compound in both the transesterification and the polycondensation reactions. Cerium and lead acetylacetonate catalysts for the transesterification of dimethyl terephthalate with ethylene glycol are disclosed by Carlson et al. in U.S. Pat. No. 3,532,671. Lanthanum compounds, such as lanthanum acetate, are disclosed by Cavanaugh et al in U.S. Pat. No. 2,820,023 to be effective transestrification catalysts for the preparation of bis(2-hydroxyethyl) terephthalate from dimethyl terephthalate (DMT) and ethylene glycol.
New process improvements which increase transesterification rates resulting in increased throughput and reduced cost of production of bis(3-hydroxypropyl) carboxylate monomer such as bis(3-hydroxypropyl) terephthalate monomer and bis(3-hydroxypropyl) naphthalene dicarboxylate monomer are of significant interest to the chemical industry.
The present invention is an improved process for making bis(3-hydroxypropyl) dicarboxylate monomer, comprising contacting a C1-C4 dialkyl ester of dicarboxcylic acid with 1,3-propanediol in the presence of a catalytic amount of at least one transesterification catalyst selected from the group consisting of compounds of yttrium and samarium at a temperature from about 150xc2x0 C. to about 245xc2x0 C.